Page:First course in biology (IA firstcourseinbio00bailrich).pdf/27

 boys and girls feel like dancing about when they go out from a warm schoolroom? What makes the flame dance or flicker when the chimney is raised by the pencils? Because it gets fresh air under the chimney.

Repeat the first experiment, in which the flame grows gradually smaller till it is extinguished. Why does the flame die out now? Is it really necessary to have fresh air in order to keep a flame burning?

To prove this further, let the candle be relighted. Place the chimney over it, now having the top completely closed by a piece of paper. Have ready a lighted splinter or match, and just as soon as the candle is extinguished remove the paper from the chimney top and thrust in the lighted splinter. Why does the light on the splinter go out? What became of the freshness that was in the air? It was destroyed by the burning candle.

Evidently there is some decided difference between unburned air and burned air, since a flame can continue to burn only in air that has the quality known as freshness. This quality of fresh air is due to oxygen, represented by O. Why was the splinter put out instantly, while the candle flame died out gradually? When the splinter was thrust in, the air had no freshness or oxygen at all, while when the candle was placed under the chimney, it had whatever oxygen was originally in the air within the chimney.

Endeavor to have this point clearly understood: that the candle did not go out as long as the air had any oxygen and that the splinter was extinguished immediately because there was no oxygen left.

Relight the candle. A former question may now be repeated: Is anything else burning besides the candle?

When the subject of the necessity of fresh air and consequently of oxygen for the burning of the candle seems